Method and apparatus for determining porosity of rock formations



2 Sheets-Sheet 1 V l l 5 5 f INVENTOR ATTORNEY l1 14"" a. l.

J. C. KARCHER s FOR DETERMINING POROSITY OF ROCK VFORMATION Filed' Aug. 9, 1935 METHOD AND APPA'RATU June 29, 1937.

s Fon DETERMINING PoRosITY oF Rocx FORMATION June `29, 1937. J. c. KARCHER METHOD AND APPARATU Filed Aug. 9, 1935 2V Sheets-Sheet 2 lnlllill ,lill/filly@ C O O O O O O O 0 O O O O .oooboooooooo INVENTOR `Patented4 June- 29119371 UNITED STATE-s' l 2,085,664l METHOD AND "APrAnATUs FOB DETER.`

MINING POBOSITY TIONS F Roon Forma- John C. Karcher, Dallas, Tex., assignor Geophysical Service, Inc., Dallas, Tex., a corporation ofl New Jersey -I 'Appiioouor'r August 9, 1'9as, 'sor1o1 No. 35.431

s choirs.` (c1. rzs-lsz) explanation of this phenomenon is found This invention relates to methodsA of determining porosity, and it has particular reference to an electrical method of determining the porosity of 'rock formations encountered by earth boring tools. f i

The principal object, of the invention is' the provision of a 'method whereby the porosity of formations encountered by a rotary drill bit may be continuously observed and recorded as drilling loproceeds.

Another object of the invention is the provision i of a method for determining the porosity of formations which utilizes the polarizing effect due to the passage of an electrical current from a metallicconductor into an electrolyte. With the foregoing objects as paramount, theinvention has particular reference to the various `steps o f the method which will become manifest as the description proceeds, taken in connection with the accompanying drawings, wherein:

Figure 1 is a diagrammatic view of one form of the invention, shown partly in vertical cross section.

Figure2 is a continuation of Figure .1.

Figure 3 is a View in vertical section of one of the insulated connections.

Figure 4 is a sectional view of the apparatus for leading current into an insulated conductor within the drill stem.

Figure 5 is a-view on the line 5 5 on Figure 4.

Figure 6 is a diagrammatic view of a modified form of the invention.

Fi'gure 7 is adiagrammatic. view of another modification of the invention, and

Figureg is a fragmentary view of a record of `the relative 'porosities of formations encountered during the drilling operation.

It is a vwell known fact that the phenomenon of electrical conduction as occurring in the earth is, with few exceptions an electrolytic one; and therefore the degree of conductivity and its manner are affected by the porosity of the materials, since theamount of electrolyte held in the formations is determined by the porosity of the formation.

When a current is caused vtoi pass from a metallic conductor intoan electrolyte or into an electrolyte thence through a boundary into a second electrolyte of. differing constituency, polarization vatsuch boundaries' will occurvas a result of the passage of such current. This polarization makes itself evident as a, counterE. M. F. which 'opposes the volt ge used to cause the current toflow and will per ist after the current inducing voltage is removed.

in Electrochemistry by Creighton and Fink 1928) Vol. I,pages 242 and 243. l

Since, as above mentioned, the electrical properties of these earth formations will be affected by their porosities, the phenomenon of polarization will valso be affected by their porosities; and, consequently a measure of thispolarization becomes a means of determining the amountof the porosity of the earth formation in question: l

Referring primarily to Figure 1, I denotes a rotary table of a conventional rotary `rig vwhich serves to rotate a Kelly joint 2, which is threadably connected to a drill stem 3. The drill stem is connected toa bit 4, and is suitably'insulated therefrom as shown. Various means may beemployed for leading an insulated conductor through the drill stem to the drill bit, the method herein illustrated being an adaptation ofv that described in detail in the copending application, Serial No.`v

to a plurality of brushes I I -which are suitably.

insulated from the housing of the unit illustrated in detail in Figures 4 and 5. The brushes I I serve to lead the current-to a slip'ring 1 I2 which isconnected through the conductor I3 and insulated bolt I4 to a conducting member I5 which, in turn has a spring connection with an insulated conductor I6. This conductor is comprised of sectionsV which are joined by insulated connecting units`illustrated in Figure 3. 'The lower end of the conductor I6 is threadably connected to a metallic drill connection I1 which is insulated from the drill pipe as shown in Figure 2. The

. drill bit 4 'is threadably connected to the drillV connection I1, thus completing the electrical circuit to ground.

In operation: the switch s is thrown so as to' close the circuit through the battery 8 and ohmmeter 9, thereby allowing vcurrent to flow for some definite period, for exampleV one minute, during which time the resistance to ground may-be read in accordance with Patent No. 1,927,664. The' switch 5 is then quickly thrown into the second position so as to close the drilling machine circuit through 'the voltmotor u; which is then promptly read. The reading of this meter thenbecomes a means of determining the amount of polariza- "tion occurring as a result of having applied an original voltage to the drilling machine circuit.

The above operation is repeated as drilling proceeds, and may be performed automatically by means of a motor driven rotary switch, in

'which event the desired infomation mayl be recorded on a recording meter, the chart being driven either by a clock or in`unison with the drilling mechanism. Figure 6 shows the manner in which this is accomplished. A rotary switch I8 is driven by a motor i9, and vis comprised of an insulating body 2U, a slip ring 2l and a segment 22 which is electrically connected to the slip ring ,2i by the conductor 23. A brush 24 makes continuous contact with the slip ring 2l, and the brushes 25 and 26 alternately make connection with the segment 2 2. When the segment 22 is in contact with the brush 25 the drilling machine circuit is closed from the binding post 21, (corresponding to the posts Bshown in Figure 1) through a'battery 28 and ohmmeter 29 to a ground 35, thus impressing the voltage of the battery upon the circuit. As the switch i8 rotates, the segment 22- breaks contact `with the brush 25, thus opening the circuit through the battery 28. The segment 22 then makes contact with, the brush 26, thus closing the drilling machine circuit through the recording meter 3l which indicates and records the polarization voltage generated in the/drilling machine circuit as a result of having previously impressed the voltage of the battery 28 upon the circuit. A 'I'he rotary switch I8 is rotated at a sufiiciently high rate oi' speed to cause the pointers of the meters 29 and Il to remain substantially at rest." .A 'direct current generator may be used instead of battery 28. The chart obtained by the use of the recording meter is illustrated in Figure 8.

The, transientobserved dueto polarization is easily distinguished fromany induced transient. In the case of a single circuit, the direction of the transient current when such current results from induction, (in this case self-induction)l will be in the same direction as theoriginal current; because the. tendency of the electro-magnetic ileld (which is the` source of the self-induced potentials) is to maintain the existing current.

Therefore, the induced current will be'in the same direction as the impressed current; whereas, thelcurrent resulting from polarization will be opposite in direction to that of the original curt rent and therefore opposite in direction to any currents resulting from self-induction of the circuit. This is evidenced by the fact that it is necessary to reverse the polarity of the -meter I0 with reference to the primary circuit. y Furthermore, the self-inductance -of the circuit .is small, because of the fact that they distance of thestake 1 from the pipe`3` is very small compared to the depth of the hole.

- Manifestly 'it is necessary that there be an interval of time between the interrupting of the connection betweenthe brush 25 and ring segm'ent 23 and time of making connection be- 'tween thebrush 26 and ring segment 23 in order toassure that there shall. .be no primary current from the batteryl 28 through the meter 3|.

Evidence that. the 'eilect observed is due to polarization and not to self-inductance is indicated by the fact that when alternating current is used, the 90 out of phase component of curimpressed current and voltage instead of lagging the impressed voltage, as would be the case if the effect were due to induction. This fact has required the use of condenser 39. Since it is desired to measure only the quadrature component of current it is necessary to throw the iield of the meter 38 into quadrature withthe Vimpressed voltage of the circuit. Thepresent invention can also be carried out by the use of alternating current as shown in Figure 7.' 4 y An alternating current generator 32- is employed to supply current to theprimary of a transformer 33, the secondary of which is con- -nected through wire 34 to a series of binding posts 35 (corresponding to the binding posts 6) on the periphery of the unit illustrated in detail in Figures 4 and 5. The circuit is completed to ground. by means of a metallic stake 36, as illustrated in Figure '7.A

When the alternating current generator 32 is operated during the drilling operation, an alternating current will flow through the circuit as described; and if there is no polarization at the bit this current will remain in phase with the applied voltage. If however, there is polarization at the bit, the counter E. M. F. resulting therefrom will produce in 'the alternati-ng current circuit a quadrature component of current leading in phase the impressed voltage by 90. When such a current is passed through the wattmeters 3"l and 38, only the power or in phase current will tend to iniiuencethe readings of the wattmeter. If however, a condenser (39 or other suitable means is introduced into the voltage circuit of the wattmeters so as to shift the phase of the current in the field coils of the wattmeters into quadrature with the impressed voltage on the drilling machine circuit, then the wattmeters will read 4the amount of wattless or quadrature current in the drilling machine circuit, which current is the current' resulting from polarization at the bit.

The method herein described is an improvement and addition to the method for measuring the resistance of the bit to ground, described in Patent--No. 1,927,664. The two methods canbe readily combined by simply adding two additional wattmeters having coils of the moving systems of the several wattmeters in series withthe drilling machine circuit and with the eld coils of the second pair of wattmeters energized without the introduction ofa series condenser. The last two instruments, when calibrated in ohms will then read 'ground resistance; and the rst two will read polarization. The entire data can be read on a single recorder with two recording elements.

The quadrature current for energizing the ponent of current in the drilling machine circuit.

Manifestly, the construction of the apparatus and the steps ofthe method described herein are capable of considerable nlocliii'ication and such modification as is considered within the scope and meaning of the appended claims is aoeaoes alsoy considered within the the invention.

spirit una intent or What is claimed is:v I I l 1. A method for determining the porosity lor sub-surface rock iormations which consists in' causing a current to iiow' through an insulated' conductor within the drill stem oi a rotary. drilling machine to" a drill bit insulated fromv said drill stem, and in measuring the amount of 10 electrical polarization resultingtherefrom.

2. A method for determining the porosity oiv sub-surface rockformations which consists in measuring the amount of polarization resulting from causing a direct current to pass through 1'5V the drill bit oi a rotary drilling machine into the ground.

, 3. Apparatus for determining the porosity of a sub-surface earth formation encounteredrby a i rotary drill blt while drilling'proceeds, compris 20ing means for causing a direct current voltage to be impressed upon the earth formation be' tween the drill bit and surface oif the ground, meansfor causing said current to ilow for a fixed interval of time, means tor suddenly removing z'the voltage which causes said current to flow,

and means for measuring and recording thepoy larization voltage resulting therefrom.

polarization resulting from causing an alternating current to now through the drillbit of a rotary drilling-machine while drilling proceeds, comprising in combination an alternating current generator connected through insulating conductors whereby to cause current to ilow throughthe bit of said rotary drilling machine to ductor being connected to a bitinsulated from.

said drill stem, means for passing an altemating current from said generator through said drill bit into the ground, and means for measuring the amount of current in the circuit which is 90 out of phase with the voltage impressed.

upon the circuit.

JOHN C. KARCHER.

, t 34 4. Apparatus-.for v determining the amount o! 

